The present disclosure is generally directed, in various embodiments, to imaging members. More particularly, the disclosure relates to various embodiments of an imaging member such as photoreceptor comprising a substrate, a charge generation layer, a first charge transport layer, a second charge transport layer, and an optional overcoat layer. More particularly, the first charge transport layer is formed from a first CTL formulation comprising an aromatic monoamine and a first polymeric film forming binder material. The second charge transport layer is formed from a second CTL formulation comprising aromatic diamine and a second polymeric film forming binder material. The imaging member has gained improved properties such as removal of anti-curl layer, desirable structural flatness, electrical properties, mechanical robustness, and flexibility, among others.
Imaging members such as photoreceptors can be provided in a number of forms, such as rigid drum configuration and flexible belt configuration. For a flexible belt, it can be either seamless or seamed. For example, the photoreceptor can be a homogeneous layer of a single material, such as vitreous selenium; or it can be a composite layer containing a photoconductive layer and another material; or it can be layered. Current layered photoreceptors generally have at least a flexible substrate support layer and two active layers. These active layers generally include a charge generation layer containing a light absorbing material, and a charge transport layer containing electron donor molecules. These layers can be in any order, and sometimes can be combined in a single or a mixed layer.
Sometimes, however, tendency to curl is a problem associated with a photoreceptor belt. Curling is believed to be the result of differential thermal expansion of the individual layers within the photoreceptor. For example, when a production web stock of several thousand feet of coated multilayered photoreceptor is obtained after finishing the charge transport layer coating/drying process, it is seen to spontaneously curl upward toward the applied coating layers. The exhibition of spontaneous upward photoreceptor web stock curling after completion of charge transport layer coating has been determined to be the consequence of thermal contraction mismatch between the applied charge transport layer and the substrate support under the conditions of elevated temperature heating/drying the solution applied wet coating and eventual cooling down to room ambient temperature. Since the charge transport layer in a typical prior art photoreceptor device has a coefficient of thermal contraction approximately 31/2 times larger than that of the substrate support, it does, upon cooling down to room ambient temperature, result in greater dimensional contraction than that of the substrate support, causing upward photoreceptor curling. What is worse, the curling may give rise to crackling, crazing and layer delamination.
To prevent curling, an additional anti-curling blocking coating (ACBC) layer may be applied to the side of the supporting substrate opposite the photoconductive layer to counteract the tendency to upward curling and ensure photoreceptor flatness. For example, US Patent Application Publication No. 2004/0072088 has disclosed several anti-curl back coating solutions. The contents of this application are incorporated entirely herein by reference. Some of the ACBC solutions were prepared in methylene chloride by combining a polyester resin (Vitel PE-200); and a polyphthalate carbonate resin (Lexan PPC 4701 having the following formula, available from GE Company), or a bisphenol A polycarbonate, or a polyether sulfone, or a polystyrene etc. The anti-curl back coating solution was then applied to the rear surface of a substrate (the side opposite the photoimaging layer) of the imaging member and dried at 135° C. to produce an optically transparent dried anti-curl back coating thickness of about 13.1 micrometers.
wherein x is an integer from about 1 to about 10, and n is the degree of copolymerization. Other ACBC solutions were prepared using styrene acrylonitrile copolymer and poly(1,4-cyclohexylene-dimethylene terephthalate) Eastar PETG copolyester; or using Makrolon 5705 and Eastar PETG; or Polysulfone, Ardel Polyarylate, or Polyphenylene Sulfone (all available from Amoco Performance Products, Inc.).
Generally, the ACBC layer must have very good wear resistance, good adhesion to the substrate and good physical stability during all applied environment. Also, the transparency and conductivity are necessary in some cases. Expensive and elaborate packaging are needed to obtain excellent ACBC for photoreceptors. Subsequent wear of the ACBC tends to cause debris in the xerographic cavity which leads to numerous problems.
As such, new solutions are needed to manufacture an imaging member such as photoreceptor, which does not require the anti-curl layer and still maintains desirable structural flatness, electrical properties, mechanical robustness, flexibility, longevity, and copy image qualities over extended use, among others.